Radar systems typically include means for transmitting an electromagnetic wave from and means for receiving a reflected signal produced when the transmitted signal is reflected by any object present in the direction of transmission. Where such systems are used in vehicles, the transmitted signal is transmitted from a vehicle, for example in the direction of travel of the vehicle, so that obstacles may be detected.
A basic pulsed radar system is shown is shown in FIG. 1, generally indicated as 10. An RF (Radio Frequency) signal from a local oscillator (LO) 12 is modulated by a pulse signal at modulation unit 14. This results in small bursts of Electromagnetic (EM) radiation at the pulse repetition frequency. The frequency spectrum produced by these bursts comprises frequency components above and below the LO frequency, at least some of the frequency components being offset from one another by an amount equal to the pulse repetition frequency. Within a given bandwidth, there can be a relatively large number of frequency components if a sharp or narrow pulse is used at modulation unit 14, or a relatively small number of frequency components if a wider or longer pulse is used. The pulse modulated EM signal is transmitted from the system 10 by a transmit (TX) antenna 15, usually after having been gain adjusted by a gain amplifier 16.
When the transmitted signal is reflected back to the system 10 by a object (not shown) in the path of the transmitted signal, the reflected signal is received by a receive (RX) antenna 18, after which the received signal is usually gain adjusted by a gain amplifier 20. The received signal is provided to a mixer component 22 whereupon the LO signal is de-modulated from the pulse signal. When the de-modulated pulse signal is inspected in the time domain (e.g. by display on a CRO) it may be observed that the de-modulated pulse signal is time delayed with respect to the pulse signal at the transmit side of the system 10. The time delay corresponds to the distance travelled by the transmitted signal before it was received at the RX antenna 18, and so the distance to the object can be determined.
The example system 10 shown in FIG. 1 includes only a single channel. To help distinguish objects more clearly, complex, or IQ, de-modulation is often used wherein there are two channels, usually referred to as I and Q, the I and Q channels being in quadrature with one another. The main principle of operation in each channel is generally the same as that described with reference to FIG. 1.
An alternative system employing a pulsed radar technique is shown in FIG. 2, generally indicated as 110. In system 110, a variable delay unit 130 is used to determine the transit time of the transmitted and reflected signal, and thus the distance to the object. In a manner similar to that of the system of FIG. 1, the signal transmitted from the transmit antenna 115 comprises a carrier signal (generated by oscillator 112) modulated by a pulse signal. The pulse signal is conveniently created using a pulse repetition frequency (PRF) generator 113 and a pulse former 111 in conventional manner. A mixer unit 122 mixes the received signal (from antenna 118) with the pulse modulated carrier signal to produce an output signal 132. The time delay unit 130 may be used to adjust the position of the pulse signal in the time domain, i.e. to delay the pulse signal used to modulate the carrier signal at the receive side of the system 110. The delay is adjusted until the output signal 132 takes a pre-determined form—this indicates that the delay has been set correctly and the set delay may be used to determine the distance travelled by the transmitted and reflected signal.
Conventional radar systems can be quite cumbersome and elaborate as they have numerous components and various different topologies. In addition, each system requires an oscillator with a sizeable amount of output power for the transmit (TX) chain and to de-modulate the received (RX) signal.
It would be desirable, therefore, to provide a system that mitigates the problems outlined above.